This invention relates to devices used in the deposition of fluids on substrate surfaces and more particularly relates to a method and apparatus for cleaning an inkjet printhead used, inter alia, in the fabrication of DNA arrays.
In the fields of chemistry, biochemistry, and molecular biology, there is a need to improve capabilities for carrying out large numbers of reactions using small quantities of materials. As a result, there is a significant and growing interest in employing array technologies where the arrays comprise an ever increasing number of distinct features on a relatively small substrate.
Many methods for making arrays of biological materials are currently available. Generally, DNA arrays are fabricated on a solid substrate by deposition of whole DNA oligomers or complementary DNA or by in-situ synthesis of DNA oligomers. Specific methods for fabricating biological arrays are summarized in international patent publication WO 95/35505. This reference discusses the xe2x80x9cdot blotxe2x80x9d technique in which a vacuum manifold transfers a number of DNA samples from circular wells to a porous membrane. In addition, DNA sequences can also be synthesized by using a photolithographic technique as discussed in U.S. Pat. No. 5,445,934 to Fodor et al., and by using a capillary dispenser tapping technique as discussed in U.S. Pat. No. 5,807,522 to Brown et al. All of these techniques suffer from inherent limitations that reduce the capacity for producing arrays accurately and reliably.
Arrays may be prepared by a variety of methods employed in the printing industry that do not suffer from the aforementioned limitations. U.S. patent applications Ser. Nos. 09/150,504 and 09/150,507 describe forming biomolecular arrays by novel methods and automated devices for moving a printhead over a print surface and for depositing the fluid composition at desired locations on the surface. Other devices used to dispense solutions are described in, for example, U.S. Pat. Nos. 5,658,802, 5,338,688, 5,700,637, 5,474,796, 4,877,745 and 5,449,754. In essence, inkjet printing processing as applied to array fabrication involves feeding a fluid composition into a dispensing chamber of an inkjet printhead and providing a stimulus repeatedly to cause the fluid composition to issue from a nozzle or orifice toward a substrate at desired locations, thus forming an array of features on the substrate surface.
Both non-uniformly deposited features and cross contamination in array fabrication can generate misleading data and thereby compromise experimental integrity. In addition, a problem with inkjet printheads in general is particulate buildup. Particulates may be introduced into an inkjet printhead when particulate-contaminated fluid is fed into printhead through a fill port as described in U.S. Pat. No. 5,777,648 to Scheffelin et al. Because the cross-sectional area of the dispensing orifice of a printhead tends to be smaller than the cross-sectional area of the fill port, it is possible to pass particulates through the fill port that cannot leave the printhead through the dispensing orifice. One way to minimize the introduction of unwanted particulate matter into the printhead is to load fluid into the printhead through the printhead""s dispensing orifice. For example, U.S. patent applications Ser. Nos. 09/150,504 and 09/150,507 disclose the transfer of a fluid into a printhead through the printhead""s dispensing orifice relying on capillary action.
Particulate buildup in the printhead is also problematic due to the repetitive nature of array fabrication. For example, when a biological array containing thousands of features is to be fabricated, the head will have to be loaded hundreds of times. During this process, the dispensing chamber of the head can become clogged with particulate matter. Especially during the wash out process, fluids tend to dry at the printhead nozzle leaving residue that was originally completely solvated or suspended as small non-agglomerated particulates in the fluid composition. When the nozzle becomes clogged with residue, droplets of fluid may fail to be fully ejected or to follow a desired trajectory. Thus, features become non-uniform in size and shape. Furthermore, once particulate matter becomes lodged within the printhead, the particulate matter provides an additional surface on which contaminants may be adsorbed or trapped thereby increasing the chance of cross contamination.
The predominant method of cleaning an inkjet printhead or xe2x80x9cdeposition devicexe2x80x9d is to flush a wash fluid through the deposition device after introducing the wash fluid via the fill port and out the dispensing orifice of the dispensing chamber. See, e.g., U.S. Pat. No. 5,589,861 to Shibata. However, the orifice of the dispensing chamber is quite small, and the orifice""s smallest dimension is typically in the range of tens of microns. Therefore, the flow rate of the wash fluid is limited by the small size of the orifice in the printhead, and low flow rates limit the effectiveness of cleaning. When flow rate is in the laminar flow regime, as is typical with ordinary flushing methods, the velocity of the wash fluid at a surface where particulate matter adheres is theoretically zero. Flushing may also cause particulate matter left in the reservoir to be transported into the dispensing chamber. In addition, particulate matter may be simply too large to be passed through the dispensing orifice. Once trapped in the printhead, particulate matter may become further embedded in the inner wall of the inkjet printhead as the result of further flushing.
Another method of cleaning an inkjet head is through sonication. Sonication is a generally well known technique in inkjet printing technology. For example, U.S. Pat. No. 5,877,580 to Swierkowski teaches sonication as a part of a method to dispense chemical fluids 25 from a capillary device. In addition, JP08085202, JP10250060, JP10250108, and JP10250110 describe the use of sonication in conjunction with inkjet printing technology.
It is well known in the art that sonication may effectively result in disintegration of particulate matter or dislodging of particulate matter from the inner surface of a printhead. U.S. Pat. No. 5,574,485 to Anderson et al., for example, provides for a method in which a transducer having a cleaning fluid thereon is placed near a nozzle. A meniscus is formed with the cleaning fluid such that the meniscus bridges the gap between the transducer and the nozzle. Energizing the transducer causes ultrasonic cleaning of the portion of the nozzle contacted by the cleaning fluid. In addition, U.S. Pat. No. 5,757,396 to Bruner provides a method for sonicating ink-carrying channels within an inkjet printhead while purging the channels with ink. However, sonication by itself is typically only effective on surfaces in contact with the medium that couples the sonic energy with the surface, usually a liquid. Furthermore, there is no guarantee that sonication will disintegrate particulate matter too large to exit through the printhead orifice.
Accordingly, it is an object of the present invention to overcome the above-mentioned disadvantages of the prior art by providing a new and effective method to clean an inkjet printhead.
It is another object of the invention to provide such a method which allows one to dislodge and remove particulates too large to pass through a dispensing orifice of an inkjet printhead.
It is still another object of the invention to provide a such method wherein particulates are dislodged and removed through reverse flushing.
It is a further object of the invention to provide such a method wherein particulates are dislodged and removed though sonication.
It is yet a further object of the invention to provide such a method wherein the printhead is dried with a gas after cleaning.
It is still a further object of the invention to provide a cleaning station for use in carrying out the aforementioned method.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, then, the present invention relates to a method for removing residue that has been deposited on the interior surface of an inkjet printhead where the inkjet printhead has been loaded with or dispensed a fluid at least once. The printhead comprises a dispensing chamber, a reservoir in fluid communication with the dispensing chamber, and a dispensing orifice for dispensing fluid from the dispensing chamber. The method involves, initially, transferring a wash fluid through the dispensing orifice into the dispensing chamber. The wash fluid is suitable for removing any remaining fluid or residue therefrom from the interior surfaces of the printhead. Then, the wash fluid is emptied from the printhead. Optional steps include substantially preventing the wash fluid from flowing out of the printhead through the dispensing orifice after the wash fluid has been introduced into the printhead, rinsing with a rinse fluid capable of leaving no residue after emptying the wash fluid from the printhead and drying with a gas, e.g., an inert gas or dry clean air, after emptying the wash or rinse fluid from the printhead.
In another aspect, the present invention relates to a cleaning station for cleaning an inkjet printhead having dispensed a fluid at least once wherein the inkjet printhead comprises a reservoir, a dispensing chamber and a dispensing orifice as above. The cleaning station comprises a fluid transfer channel for transferring fluids or gases from one or more external sources through a transfer port into an inkjet printhead. In use, the transfer channel is placed against the printhead so that the transfer port and the dispensing orifice of the printhead are in fluid communication, enabling transfer of fluids and gases from the cleaning station into the dispensing chamber through the dispensing orifice. The cleaning station also comprises a wash fluid container for holding the wash fluid, an optional rinse fluid container for holding the rinse fluid, and an optional gas container for holding the inert gas or dry clean air, each capable of fluid communication the fluid transfer channel. Furthermore, the cleaning station comprises a vacuum pump that can be attached to the inkjet printhead for reducing pressure within the printhead such that fluid is drawn into the printhead through the transfer port and dispensing orifice of the printhead. A sealing material surrounding the periphery of the transfer port is provided to form a vacuum seal around the dispensing orifice. Optionally, the cleaning station further comprises means for sonicating the wash fluid.
Alternatively, the cleaning station can use a wash fluid holder (for example, a saturated capillary medium such as a sponge, or open container) which can be positioned such that wash fluid held therein is in communication with the dispensing chamber through the dispensing orifice (such as by being directly in contact with the orifice). Positioning can be accomplished, for example, by a suitable transporter which moves the printhead, fluid holder, or both of them. A pressure control system is provided to create a pressure differential across the dispensing chamber and orifice such that wash fluid in communication with the orifice is transferred through the dispensing orifice into the dispensing chamber. The pressure control system may include a positive pressure source acting on the wash fluid and/or a negative pressure source (which reduces pressure to less than atmospheric pressure) acting on the dispensing chamber (either of which source may, for example, be a pump).
In still another aspect, the present invention relates to a cleaning station as above except that the vacuum pump is replaced with a means to inject fluids or gases into the dispensing chamber through the dispensing orifice.
In a further aspect, the present invention relates to a cleaning station as above wherein the cleaning station further comprises a flexible capillary medium that assists in presenting or conveys the wash fluid to the printhead.
Particularly when the fluid contains a polymer (such as a polynucleotide) or a polymer precursor (such as a nucleoside compound which forms a unit of polynucleotides synthesized on a substrate from the nucleoside compounds), the same methods can be used but with wash fluid being transferred in any direction from the external source through the dispensing orifice and dispensing chamber (for example, from the dispensing orifice into the chamber or from the chamber through the orifice) into a waste line or waste container. As before, the wash fluid may be sonicated while the wash fluid is in contact with a surface of the printhead where cleaning is desired. Optionally, such a method may additionally include using the printhead to dispense droplets of the polymer or monomer to form at least a portion of an array (such as a polynucleotide array) prior to the wash fluid transfer and cleaning.